Electric potential difference between a battery's + terminal and the ground

  • #76
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in this model which are actually the two 'plates' of the 'battery-Earth' capacitor system ?
The metallic conductor of each electrode in the battery.

In practice (if 'in practice' makes any sense in this scenario with virtually zero actual capacitance), assuming the battery case is metallic which it probably is, there will be a capacitance between the outer case of the battery and Earth (the two 'plates') then you will effectively have two further capacitors in parallel (but in series with the case-Earth 'capacitance') to the battery electrodes

Not sure to understand the model: how is the voltmeter connected here ? Are you considering a simple 'RC' series circuit ?

Thanks
An ideal voltmeter has infinite resistance. But it is impossible for a real world voltmeter to have infinite resistance. They usually come with 1 MOhm or 10MOhm internal resistance, so that'll be your 'R'.

[In fact, I often measure kV/ua stuff with cheap multimeters (they tend to blow up on a regular basis, no point buying expensive ones) and I don't bother with the current selections, I just pass the current straight through the 'voltmeter' setting, giving me ua = volts based on a 1 MOhm internal resistance.]

FWIW There is no such thing as an infinite resistance. It's funny really, because intuitively you'd expect 'something' to be a perfect insulator and 'nothing' to be a perfect conductor, but reality treats us to something non-intuitive that there is no such thing as a perfect insulator, but there is such a thing as a perfect conductor! Your voltmeter will always pull the battery terminal to ground when you try to measure it, there is nothing connected to the other terminal to stop that. A capacitance would slow that down, but not stop it.
 
  • #77
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No, we are not considering a simple RC circuit. After three pages of this thread, do we have say, yet again, that THERE IS NO CIRCUIT?
yes got it....there is no galvanic closed circuit through the Earth.

We have a capacitor with one terminal connected to the battery and the other terminal connected to the earth, and a voltmeter with its probes on each side of the capacitor. And this is equivalent to the configuration you started with, one probe on the battery and the other on the earth; it's only interesting to consider it because it's easy to buy a capacitor with much more capacitance than in your original setup.
here, let me say, we are basically considering a simple RC parallel where R is actually the internal voltmeter resistance
 
  • #78
That's a bit typical of Tesla publications. No actual figures quoted and loads of Astrological style.
I guess he was writing for the general public at the time. However, I have seen Youtube videos of people putting wires at the top of a pine tree and measuring a potential when putting a meter from that lead to a grounded lead. I don't recall seeing any astrology in that article.
 
  • #79
gleem
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I have seen Youtube videos of people putting wires at the top of a pine tree and measuring a potential when putting a meter from that lead to a grounded lead.
Could you find it URL so we could see it?
 
  • #81
This is not the one I saw before, but still somewhat interesting. The other one will take some searching, but I think it was John Hutchison doing the experiment.
 
  • #82
sophiecentaur
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I don't recall seeing any astrology in that article.
I referred to astrological style and not astrology. Tesla did an awful lot of waffling and had his audience enthralled. I'm amazed that the 'enthraldom' seems to persist to this day. True, he made a choice about adopting the use of AC Power; lucky guess? There was a lot of 'general ignorance' about 'electricity' at the time and fortunes were won and lost on the strength of non-engineering hunches. ("So what's different now?", I hear you cry - but PF didn't exist in those days)
We haven't been shown that article but another article . . . . . .
This is not the one I saw before, but still somewhat interesting. The other one will take some searching, but I think it was John Hutchison doing the experiment.
He says he's measuring "nine point nine volts" when the meter appears to read 0.99V. He has actually posted it! What does that say about experimental method? How long did the PD exist for and what was the drain current?
 
  • #83
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He says he's measuring "nine point nine volts" when the meter appears to read 0.99V. He has actually posted it! What does that say about experimental method? How long did the PD exist for and what was the drain current?
Looks like he is using galvanized screws. I believe the emf of copper- zinc galvanic cell is about 1V. The man is an idiot.
 
  • #84
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Hi,

I've a question about electricity in the following scenario: consider an accumulator (e.g. a 9V battery) and an analog/digital voltmeter having a probe connected to the accumulator + clamp and the other to the ground (for instance connecting it to a metal rod stuck in the ground).

Do you think there will exist a electric potential difference as measured by the voltmeter ?

Thanks.
Answer to your question in one word is "no"
To clarify further we may split the question into two parts
1) Do you think there will exist a electric potential difference(between +clamp and earth)? Answer is "yes"
2) Can the above potential difference be measured by voltmeter? Answer is "no".Because voltmeter needs a closed circuit to work
 
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